A Study of Several Typhoons in the West Pacific, 1945" CAPT. KENNETH P. KIDD, A.C. Cherry St., Alcoa, Tennessee AND CAPT. CHARLES K. REED, A.C. 622 Delaware Ave., St. Paul, Minn. N THIS PAPER is presented a brief study Storm Grace formed south of Marcus Is- I of some of the typhoons affecting mili- land about 15 August 1945, moved in a NW tary operations in the Southwest Pa- direction, and entered SE Honshu near To- cific in 1945 with an emphasis upon their kyo on the night of 22 August, giving wide- origin and movement. Selected analyzed spread rain and a minimum barometric pres- daily surface charts are included. The sure near Tokyo of 986 mb. The direction temperate-latitude areas of the analyses have and speed of movement of Grace indicated been checked with data later obtained from the presence of a large high-pressure cell the files of the Japanese Central Meteoro- to the northeast of the storm—a fact that logical Observatory. Excellent data from was helpful in the forecasting of the move- Army and Navy typhoon reconnaissance ment of Ruth. Upon passage over Honshu planes enabled reliable lifixes'' of the posi- Grace filled rapidly, and her influence on tions of the typhoon centers to be obtained. the other typhoons declined accordingly Since no detailed records were available from after 23 August. land stations over which the centers of the At the time of formation of Grace the ITC typhoons passed, the actual maximum in- (intertropic zone of convergence) extended tensity of the typhoons was estimated from through Luzon and into a large area of low the winds and extrapolated pressures re- pressure and weak winds in the vicinity of ported by the aircraft. On the charts, sur- 17°N 130°E. Development of the low did face data include wind, sky cover, weather, not take place for several days because the pressure and 24-hour pressure change. flow of easterlies did not penetrate west of Wind speeds are represented by 10-knot 135°E and because the westerlies were un- barbs. Heights of winds-aloft reports are usually weak. given in thousands of feet. Aircraft reports Gradually the SE trades in the Palau and include weather and the height of plane (in southern Philippines area retreated in favor hundreds of feet), plotted above the time of an increasing flow of Indian westerlies, (OCT). which by 20 August had swept over the entire Philippines and was continuing ENE TYPHOONS RUTH AND SUSAN T (ALSO TESS in a narrowing stream. On this day a fresh AND GRACE), 22-27, AUGUST 1945 surge was noted in the westerlies, marked by (Figs. 2 to 4) winds of 25-40 knots over the South China Sea. These four tropical cyclones of storm of typhoon intensity that appeared almost si- On 21 August Grace was located 250 miles multaneously present a most spectacular and NE of Iwo Jima with a trough extending interesting example of formation and move- SW to join the ITC. At this time the low ment. The presence of typhoons Ruth and pressure area east of Luzon was greatly elongated along the ITC near 21 °N. Easter- Susan caused a 48-hour delay in Supreme lies to north of the low were weak (10 knots, Allied Commander MacArthur's plans to up to 15,000 feet) while the flow of Equa- land occupation forces in Japan. torial air south of the low had strengthened * Published with permission of the War Department. to 20 to 25 knots. As the surge of Equa- t The Army Air Forces Weather centrals in the SW torial air turned NEward near the eastern Pacific in 1945 began the custom of identifying tropical storms by first names of wives of their commanding end of the elongated low, the pressure began officers.—Ed. Unauthenticated | Downloaded 09/24/21 10:51 AM UTC to fall in tlie forward left edge of the surge third typhoon (Tess) was found 75 miles and storm Buth developed there on 22 Au- south of Hong Kong on 24 August moving gust (FIG. 2). It has been noted in other NNEward. These typhoons developed very instances that when a strong surge of Equa- rapidly and in each case the area of strong torial air juts sharply into another wind winds had but a short radius. This behavior stream to the north, tropical cyclonic devel- is quite in contrast to that of some other opment has taken or is taking place. 1945 typhoons of the SW Pacific, which de- The mountains of northern Luzon act as veloped only very slowly by a gradual a barrier to the flow of the SW monsoon, strengthening of the winds about a large sometimes splitting the stream and causing area of low pressure and often with the the formation of a small typhoon just NW strongest winds appearing first a great dis- of Luzon. Streamline charts for the 8000- tance from the center. foot level for 22 August can be analyzed to Also of particular interest in the cases of show three tongues of SW monsoon: one Buth and Susan is the unequal distribution wide stream flowing across the southern of strong winds around the periphery of the Philippines toward the newly formed storm typhoons. In both typhoons the strongest Buth; a second narrow stream flowing winds were first found in the southern quad- swiftly up the west side of Luzon (winds rants and gradually moved counterclockwise at Laoag reached 50 knots from the SSW into the NE quadrant (FIGS. 2 and 4). below 10,000 feet) ; a third narrow stream Relatively weak winds were found in their turning NNEward around 17 °N 114°E. NW quadrants, and also in the area between Each of the tongues was associated with the the typhoons where horizontal shear pre- development of a typhoon in the ITC, for a vented strong opposing winds. The migra- second typhoon (Susan) was found near tion of the strong-gradient region to the NE 22°N 124°E on the morning of 23 August quadrant of Buth was associated with the (FIG. 3) moving in an ENE direction and a disappearance of the trough leading to Grace Unauthenticated | Downloaded 09/24/21 10:51 AM UTC (FIG. 2) and with the blocking action of pressures and steep pressure gradients indi- the high-pressure area northeast of Iwo Jima. cated that the strongest winds were migrat- The migration of the area of strong winds ing into the NE quadrant. about Susan, however, resulted from the Ruth reached typhoon intensity before movement of Ruth to the north. entering Honshu, with winds of 60 to 65 The trajectory of each typhoon paral- knots reported near the center and with an leled step by step approximately the direc- estimated central pressure of 986 mb. tions of the strongest '' environment-winds'' Susan was somewhat more intense with 80- near its periphery. The initial movement knot winds reported 26 August and an es- in each case was ENE with a gradual re- timated central pressure of 980 mb. In- curvature to the NNW, when the rising sufficient data are available from coastal Unauthenticated | Downloaded 09/24/21 10:51 AM UTC stations of southern Honshu for a more and dissipated within an area covered by accurate picture of the intensity of Rutli and Army and Navy typhoon reconnaissance Susan as they passed inland. Both typhoons planes—the complete life-history lasting 8 passed over the mountains of Honshu and days. recurved NE across the Sea of Japan. In September-October a bulge of the ITC north of its normal position in the Marianas TYPHOON JEAN, 25 SEPTEMBER TO is always viewed with suspicion, especially 2 OCTOBER 1945 if the ITC between the Marianas and the {Figs. 5 to 8) Philippines is at the same time south of the normal position. The northward bulge of Jean was one of the five most severe ty- the ITC is owing to the advance or surge phoons of the Pacific in 1945. She appears of the Equatorial air, and is also assisted in this study because she formed, developed, by any SEly component of the trades where Unauthenticated | Downloaded 09/24/21 10:51 AM UTC they are deflected 011 the east side of a pass- On the 700-mb chart there was a split in ing Easterly or Induced Trough. The the Pacific High near 140°E, the western southerly position of the ITC west of the cell being centered about 20 °N 130 °E. bulge indicates that the northern trades are Slightly to the east of this 700-mb trough, a blowing from ENE or NE in that area and surface trough extending NNE from the thus in a position favorable for producing ITC at its northward bulge was moving cyclonic shear with respect to the Equatorial slowly to the west. The easterlies between air. On 24 September such a counterclock- Philippines and east of Guam were blowing wise shifting of the orientation of the ITC at around 10 knots, up to 20,000 feet. The was observed. The ITC now extended from base of the westerlies dipped down to 30,000 Truk to a northermost position at 12 °N feet over the Marianas. Indian westerlies 142°E, thence WSW toward Samar. in the South China Sea had been diverted Unauthenticated | Downloaded 09/24/21 10:51 AM UTC into a small storm approaching Hainan trough which was located west of that sta- island, so that the flow of air south of the tion in the levels below 20,000 feet and to ITC was very weak in the area between east of the station at 30,000 to 40,000 feet.